Gear checking machine having a frictionally driven support table and position encoder

ABSTRACT

A gear checking machine for measuring the involute profile and the helical lead of a gear having a support table which is coupled to a base disc that is driven by a friction drive mechanism is disclosed. The friction drive is achieved by means of a small drive wheel which drives the large base disc which has its shaft coupled to the rotatable support table. An encoder having a small drive wheel which is frictionally driven by the large base disc is employed whereby the encoder supplies electrical output signals representative of the degree of rotation of the support table and the gear. Involute and lead checking probes are mounted so they may move in the horizontal and vertical directions, respectively, relative to the gear being checked.

BACKGROUND OF THE INVENTION

This invention concerns a gear checking machine which is particularlyuseful in measuring helical lead and involute gears, especially largegears those on the order of 40 to 60 inches or more in diameter. Themeasurement of the helical lead and of the involute both require anaccurate timed relationship between a rotating axis and linearly driventest probe. Prior art involute checkers utilize a ratio bar inconjunction with a master base circle sector or disc. This type ofmachine had physical limitations which placed severe limitations on theaccuracy of the machine and the configuration of the gear support tablein the measurement of large gears on the order of 40 to 60 inches ormore in diameter. The timed relationship between a rotating axis andlinear motion of the helical lead testing machines of the prior art isgenerally accomplished by a sine bar unit which transmits an accurateangular measurement. Machines incorporating these device are to be seenin U.S. Pat. Nos. 2,787,060 and 2,998,657.

The present invention eliminates the ratio bar and sine bar and utilizesa large disc or base circle which is coupled to the gear support table.The large base circle is operatively attached to an encoder whichaccurately registers by electronic pulses the angular or rotary movementof the base disc. The input of this encoder advantageously is achievedby utilizing a very small diameter disc which is normally driven by theouter periphery of the large base disc. This large ratio between thebase disc and the encoder disc provides a large range of accuracy indetermining the angular movement of the disc.

Two simple discs with properly calculated diameters rotating with eachother can provide a much wider range of ratio and accuracy than thatobtainable by another device.

A number of advantages are gained by this device in proportioning,manufacturing and in assembly. These are:

1. Flexibility-- large ratio range can be obtained.

2. Changes can be readily made by changing diameter of mating disc.

3. Round configuration-- easy to make-- easy to manufacture.

4. Exact ratio can be obtained by simple regrinding of the smaller disc.

5. Positive drive can be obtained by holding the discs in contact bymeans of springs, adjustable pressure bar, weights, etc.

In summary, incorporation of base disc principle in conjunction withstepping motors and gear boxes, provides a wide range of proportioningat a very low cost not possible with other known methods.

It is therefore an object of the present invention to provide a gearchecking machine having a rotatable table for supporting a gear to bechecked which is coupled through a shaft to a large diameter base discwhich is frictionally driven by a small diameter wheel that is inengagement with the periphery of the large base disc wherein the largebase disc in turn frictionally drives a small wheel which is coupled toa position indicating encoder.

It is an additional object of the present invention to provide a gearchecking machine which has a rotatable table for supporting a gear to bechecked wherein the table is coupled to a large diameter base dischaving a circular cross-sectional configuration, the periphery of whichis utilized to drive a disc of a predetermined diameter which issubstantially smaller than the diameter of the base disc and which iscoupled to an encoder to provide a signal which is indicative of thedegree of rotation of the support table.

It is a further object of the present invention to provide a drive andencoding system for a gear checking machine in which a table forsupporting the gear to be checked may be driven at a rate which may beeasily varied by changing the diameter of a small drive wheel that itutilized to frictionally drive a large base disc which is coupled to therotatable table and the resolution of the encoder, which emits signalswhich are representative of the rotation of the table, may be easilyvaried by changing the diameter of a small wheel which is frictionallydriven by the large diameter base disc.

Other objects and advantages of the present invention will be apparentto those skilled in the art from the disclosure of this invention.

DESCRIPTION OF THE DRAWINGS

The invention is illustrated in the drawings in which;

FIG. 1 is a perspective view of the gear checking machine of the presentinvention which shows the large base disc, the friction drive mechanismand the encoder of the present invention; and

FIG. 2 is a block diagram of the control circuitry of the gear checkingmachine of FIG. 1.

TECHNICAL DESCRIPTION OF THE INVENTION

A perspective view of the gear checking machine 10 of the presentinvention is shown in the FIG. 1. The gear that is to be checked isplaced on the large table 12 which is supported by the base 14. Thetable drive motor (not shown) is mounted within the base 14 to rotatethe table 12 at a controlled rate. The involute measuring probe 16 ismounted for linear horizontal movement along the involute slide 17 bythe involute probe drive mechanism 18. The lead measuring probe 20 ismounted for linear movement in a vertical direction in the elongatedslot 19 by the lead probe drive mechanism 22 which is supported by thebrace 24. The probes 16 and 20 may be pressure sensitive probes of thetype generally employed in the gear checking art in which pressureapplied to the sensing ends 16a, 20a, respectively, of the probes 16 and20 control the movement of a magnetic slug in a variable differentialtransformer (not shown) so as to develop an electrical signal which is afunction of the magnitude of the pressure on the measuring probe.

On the bottom of the support table 12 and within the base 14, a largecircular base disc 26 is secured to the shaft 27 which is in turncoupled to the table 12 so that the table 12 is driven in rotation withthe disc 26. Suitable conventional bearings (not shown) are provided toallow for easy rotation of the table 12. An encoder 28 of a conventionaltype may be mounted to the base 14 by bolts or the like which areinserted into the holes 31 in the arms 33, and has a small driven wheel30 which is driven by the large base disc 26 to provide encoded signalswhich are representative of the angular rotation of the support table12. The diameter of the base disc 26 is approximately equal to thediameter of the table 12 and preferably at least 10 times as large asthe diameter of the encoder wheel 30 to insure that the encoder willrespond to relatively small angular rotations of the table 12.

In order to provide for accurate measurement of the involute and thehelical lead of a gear, it is necessary that the movement of the supporttable 12 be accurately synchronized with the linear movement of theinvolute probe 16 and the lead probe 20. The electrical system of thepresent invention which achieves the desired control is shown in blockdiagram in FIGS. 2 and 3.

In the gear checking machine of the present invention either the helicalinvolute or the lead may be checked at a given time. Selection of eitherthe lead or involute measuring function is made by the multiple gangsection switch 36 which is shown in the FIGS. 2 and 3. The position ofthe switch 36 in FIGS. 2 and 3 is shown at the lead checking position.When the switch 36 is in the lead checking position the vertical motionof the lead probe 20 is synchronized with the rotation motion of thetable 12. The driving system for the table 12 is achieved by use of apulse generator 38 which is coupled to a stepping motor drive system 40which supplies driving pulses to the spindle drive stepping motor 42.When the switch 36 is in the lead measuring position, the relay 44r willclose the contacts 44k and this will energize both the relays 50r and52r. The relay 50r acts to close the contact 44c while the relay 52rcloses the contact 52c which allows a recorder 80 to be driven at asynchronous rate, as is described subsequently in more detail. When theswitch 36 is in the involute position the relay 54r is energized ratherthan the relay 44r. This causes the contacts 54k to close thereby againenergizing both relays 50r and 52r, and, thus, again closing contacts44c and 52c.

The spindle drive motor 42 is energized and receives driving signalsthrough the cable 43. As the spindle drive motor 42 is stepped, theoutput shaft 45 of the motor 42 is driven. The shaft 45 drives the gearbox 47 which in turn drives the shaft 49 which is coupled to thefriction drive wheel 51. The gear box 47 preferably provides a reductionrate of at least 10 to one, and the diameter of the drive wheel 30 ispreferably equal to the diameter of the encoder wheel 30. The highresolution of the drive and encoding system of the present invention isillustrated by typical parameters for the components of the system. Forexample, the diameter of the base disc 26 may be 40 inches. The steppingmotor 42 then may make one revolution resulting in one revolution of theencoder 28. If the encoder 28 produces 25,000 pulses in one revolutionof disc 30 then 10 revolutions or 2,500,000 pulses will be produced whentable 12 is revolved one turn. It is seen, therefore, that the encodersystem of the present invention is one in which each output pulse of theencoder 38 may represent a relatively small amount of angular rotationof the gear being tested. The rotation of the encoder 28 provides acoded representation of the rate of angular displacement of the table 12which consists of a series of pulses of a rate which corresponds to therate of rotation of the table 12. This series of pulses from the encoder28 is supplied through the cable 53 to multiplier 60 which emitsmultiple output pulses for every one input pulse that it receives.

The purpose of the rate multiplier 60 is to increase the speed of thelead profile probe 20. It is noted that when the switch 36 is in theinvolute position the rate multiplier 60 is bypassed and the outputpulse from the encoder 38 is fed directly to the rate multiplier 62.This is because the lead measuring probe 20 must be driven at a fasterrate than the involute measuring probe 16 for long leads. Aside fromthis factor, however, both the involute and the lead probes arecontrolled in substantially the same manner.

The purpose of the rate multiplier 62 is to provide a series of outputpulses which occur at a predetermined fractional rate of the inputpulses from the encoder 28. The rate multiplier 62 is constructed tomultiply the signal from the encoder 28 by a variable preset factorrather than by a constant factor. In the checking of any given gear itis necessary to establish either manually, or by means of a recordedprogram, the appropriate preset factors that are to control the ratemultiplier 62 for both the involute and the lead checking cycles. Thesefactors are digital numbers which when contained in the binary counter64, which is coupled to the rate multiplier 62, establish theappropriate frequency multiplication factor to synchronize the speed ofthe lead and involute probes 16, 20 with the rate of rotation of thetable 12. The rate multiplier 62 is a known type of device, and onesuitable type of circuit for use in the present is the K1848 multipliersold by Digital Equipment Corporation of Maynard, Mass.

The manner in which the preset multiplication factor is established inthe binary counter 64 can be seen by reference to the FIG. 3. Thedesired digital number which is needed to establish the appropriateratio of the rate multiplier 62 may be set into the digit switches 66.The pulse generator 68 then supplies pulses to the binary coded decimal(BCD) counter 70, which is initially set to a count that is establishedby the digit switches 66. The BCD counter 60 counts down to zero. Adigital readout 72, which is coupled to the counter 70, supplies acontinuous visual indication of the contents of the counter 70. Thebinary counter 64 is initially at a zero count when the BCD counter isset at the count of the digit switches 66. The binary counter 64 countsup and continues counting until the count established by the digitswitches 66 has been reached, at which time the count in BCD counter 70will be zero.

With the correct multiplication factor for the rate multiplier 62 beingestablished by the count in the counter 64 the rate multiplier 62 willsupply pulses to a conventional stepping motor drive circuit 74 inaccordance with the preset factor in the switches 66 thereby providingthe required synchronization of the linear motion of the probes 16, 20with the rotation of the table 12. When the switch 36 is in the leadmeasuring position, the relay 44r is energized and the contact 44s isclosed which allows the stepping motor drive circuit 74 to drive thelead slide drive stepping motor 76 and the lead drive mechanism 22through the closed contacts 44s. On the other hand, when the switch 36is in the involute measuring position the contacts 44s are open and thecontacts 54s are closed which allows the stepping motor control circuit74 to drive the involute slide drive stepping motor 78 and the involutedrive mechanism 18 through the closed contacts 54s.

In order to obtain a permanent written record of the gear being checkeda recorder 80 is employed. The recorder 80 is driven by a recorder drivestepping motor 82 which is supplied pulses from the stepping motor drivecircuit 84 through the contacts 52c. The recorder stepping motor driverate is generally different according to whether the involute probe 16is being driven or the lead probe 20 is being driven. This is achievedthrough the switch 36 which allows either the involute rate multiplier86 or the lead rate multiplier 88 to be coupled to the stepping motorcontrol system 84. The rate multipliers 86 and 88 are similar to themultiplier 60 in that they multiply the incoming pulses by a fixed ratioto provide output pulses with a frequency which is suitable forsynchronizing the recorder 80 with linear motion of the probes 16, 20and the rotational motion of the table 12.

The encoder system of the above-described invention provides a number ofadvantages over conventional encoder system. The encoder system allowsfor the use of a relatively inexpensive encoder 28 to produce 10 or moretimes as many pulses as could be produced by the usual method ofmounting. The usual method of mounting would put the encoder on the sameaxis as the table 12. An encoder mounted in the usual fashion on theaxis of table 12 would have to produce 10 times as many pulses and wouldbe very large and expensive, perhaps eight or 10 times more expensive todo the same job.

Also mounting the encoder to the side of the base disc 26 below thetable 12, as shown in FIG. 1, allows for a large hole 13 in the table12. This is very important because it allows for checking of long shafttype gears by dropping the shaft down the table hole 13 and resting thegear on the table 12. Without a large hole in the gear support table theutility of a gear checking instrument is severely limited.

The invention is claimed as follows:
 1. A gear checking machinecomprising a frame, indicating means, a table rotatably mounted in saidframe for supporting a gear to be checked, sensing means mountedadjacent said gear for supplying a signal to said indicating means whichis indicative of the surface variations of said gear, a first shaft, arelatively large diameter circular disc coupled to said table by saidfirst shaft and supported; below said table by said first shaft, firstand second small circular wheels each having a diameter substantiallysmaller than the diameter of said large disc, said first small wheelhaving its periphery in engagement with the periphery of said largedisc, .Iadd.a second shaft coupled to said first small wheel, saidsecond small wheel having its periphery in engagement with the peripheryof said large disc, .Iaddend.disc drive means coupled to said secondshaft for simultaneously revolving said first and second small wheels,said table and said large disc, sensing drive means for driving saidsensing means in synchronism with said table and said disc, a thirdshaft coupled to said second small wheel and encoder means coupled tosaid third shaft for supplying output signals which are a function ofthe rotation of said table.
 2. A gear checking machine as claimed inclaim 1 wherein said first and second small wheels are of approximatelythe same diameter.
 3. A gear checking machine as claimed in claim 1wherein said drive means comprises a gear reduction means coupled tosaid second shaft.
 4. A gear checking machine as claimed in claim.[.2.]. .Iadd.3 .Iaddend.wherein said drive means comprises a steppingmotor having an output shaft which is coupled to said gear reductionmeans.
 5. A gear checking machine as claimed in claim 4 wherein saidfirst and second small wheels are of approximately the same diameter.